This invention relates generally to devices commonly referred to as angle sensors, clinometers or accelerometers and more particularly to improved angle and angular acceleration sensors that utilize a test mass/suspension element manufactured by means of a chemical milling process. The position of the test mass is measured by capacitive, inductive or optical means, for example, utilizing plates mounted on one or both side of the test mass. The angle sensor of the present invention measures the angle between its case and the gravity, or total acceleration, vector. In an alternative embodiment of the invention, angular acceleration may be measured. Either device may be constructed to operate in an open loop or closed loop configuration.
Various angle sensors are known in the prior art. Typically, they comprise fluid filled electrolytic or capacitive devices. Exemplary of the electrolytic devices are the Spectron and Fredericks glass vials using platinum electrodes and a fluid comprising alcohol with dissolved metallic salts. These prior art devices suffer from relatively high cost, slow response time, and fragility. Exemplary of the prior art fluid filled capacitive devices is the Lucas Accustar, which also suffers from slow response time, limited range when used as an accelerometer, and relatively poor measurement repeatability and stability.
It is therefore the principal object of the present invention to provide improved low cost angle and angular acceleration sensors exhibiting virtually unlimited range and excellent short and long term stability and high frequency response.
This and other objects are accomplished in accordance with the illustrated preferred embodiments of the present invention by providing a layered sandwich sensor structure having a central sensing plate, left and right insulating spacers positioned outside the sensing plate, left and right driver plates positioned outside the insulating spacers, and left and right molded plastic housing shells positioned outside the driver plates for sealing the sandwich sensor structure. In an angle sensor embodiment of the invention, the sensing plate includes a peripheral frame and a central plate area mechanically connected to one side of the peripheral frame by way of a pair of torsion bars that serve as a hinge to allow the central plate area of the sensing plate to rotate toward and away from the driver plates sanwiched on either side thereof. In an angular acceleration sensor embodiment of the invention, the sensing plate includes a peripheral frame and a central plate area divided into upper and lower halves, each of which is mechanically connected to the frame by way of a pair of torsion bars that extend inwardly from two opposite sides of the frame and that similarly serve as a hinge to allow the upper and lower halves of the central plate area to rotate toward and away from the adjacent driver plates. Though the preferred embodiments of both the angle and angular acceleration sensors of the present invention employ torsion bars to hinge the central plate area, other beam configurations which allow the central plate area to be deflected toward and away from the driver plates may be utilized.
The atmosphere inside either the angle or angular acceleration sensor may comprise air, an inert gas, or a dielectric fluid for increased capacitance and/or increased damping in high vibration environments. Further, it is not required that two driver plates and two spacers be employed in the angle and angular acceleration sensors of the present invention. A simplified yet functional sensor may be constructed using only one driver plate, one spacer, and one sensor plate.